1. Field of the Invention
The present invention relates to single and multi-layer polytetrafluoroethylene (PTFE) peelable sheaths and methods for manufacturing and use of such sheaths. Sheaths of the present invention are particularly suited for use as cannulas and other medical introducer devices.
2. Background
Splittable cannulas have been employed in various medical and surgical procedures for inserting catheters, guide wires and the like into patients. A typical procedure provides for insertion of a dilator or needle into the vasculature of a patient while encased within a splittable sheath. After insertion, the dilator or needle may be removed leaving the sheath protruding from the patient""s vein. An ancillary medical device, e.g., a diagnostic or therapeutic catheter or guidewire, is then threaded through the sheath into the patient. The encasing sheath is then longitudinally sheared and removed from the catheter or guide wire and the patient such as by applying opposing force to opposed wings or tabs of the introducer device. See e.g., U.S. Pat. Nos. 5,334,157; 5,221,263; 5,141,497; 5,098,392; 4,772,266; and 4,243,050; and WO 97/14456 and WO 97/14468.
For ease in shearing and overall handling of the device, it is desirable to employ a sheath of minimal thickness, e.g., thin-walled, having some degree of flexibility.
Notable disadvantages have been observed when using devices which incorporate a xe2x80x9ctear-awayxe2x80x9d or splittable sheath. For example, easy and non-traumatic removal of the sheath is critical. It is possible that the sheath may not tear evenly or completely, thereby necessitating additional maneuvering and application of excessive force to the device. Excessive movement or force exerted upon the sheath is likely to cause damage to the vasculature of the patient. There is also the potential of accidentally dislodging the catheter from its inserted position while trying to remove the sheath.
Many design configurations and processes have been investigated in an effort to overcome the various deficiencies observed in devices of the prior art which incorporate a peelable sheath.
For example, certain devices and methods were developed which employed a skiving process in order to produce peelable sheaths. Using such a process, approximately one half of the wall thickness of the tubing material, e.g. a plastic, typically is cut away in a longitudinal direction. In that way, a weak spot in the tubing wall is presented where the tubing material can be peeled.
U.S. Pat. No. 4,306,562 (Cook) discloses a flexible, tear apart cannula which may be removed by pulling tabs on opposite sides of the cannula following insertion of a catheter or other device into the body. That patent reports that the cannula tears readily in a longitudinal direction along the length of the structure because it comprises material having a longitudinal orientation, e.g., polytetrafluoroethylene or other plastics. The longitudinal orientation is achieved using a standard extrusion process, and a slitting operation is used to create the tabs for pulling the cannula apart. See also U.S. Pat. No. 4,581,025 (Cook).
It has been shown, however, that the cannulas produced in accordance with the Cook patents present certain limitations. For example, despite the fact that the tubing material has a longitudinal orientation, peelability still can be problematic. Additionally, certain additives which are added to the preferred tubing material, TEFLON (TEFLON is a registered trademark of DuPont for polytetrafluoroethylene), for X-ray visualization cause discoloration when the sheath is tipped by conventional thermal processes. Thus, the Cook devices may only be produced in dark colors (e.g., gray and black) that hide such discoloration.
U.S. Pat. No. 5,318,542 describes another process for producing a split cannula device having predetermined break lines which reportedly provides enhanced disassembly of the cannula. Predetermined break lines are produced by a non-metal-cutting shaping process, thereby enhancing uniformity of the predetermined break lines and reducing the force needed to disassemble the cannula. See also, U.S. Pat. No. 5,104,388.
There remains a need for improved medical introducer devices which incorporate a peelable sheath to facilitate smooth entry of an ancillary medical device into a patient, and easy and non-traumatic removal of the sheath following insertion of the ancilliary medical device.
It would be desirable to develop a multi-layer sheath configuration, e.g., an inner layer which permits visualization by X-ray or fluoroscopic procedures, and an outer layer that is resistant to discoloration by thermal processes. Such a configuration would be desirable in that the device could be produced in a variety of colors including white, blue or any other thermally stable color.
It also would be highly desirable to develop methods for the manufacture which produce single and multi-layer peelable sheaths with superior tear properties. More specifically, it would be highly desirable to develop methods for the manufacture of such sheaths which do not rely on mechanical skiving of the sheaths. We have found that skiving does not always produce tubing with good peel properties, especially when using tubing materials such as polytetrafluoroethylene.
We have now produced medical introducer devices which incorporate a single or multi-layer polytetrafluoroethylenepeelable (PTFE) sheath.
Preferred sheaths of the invention are characterized in part by being readily splittable along their length (longitudinally) without use of any type of mechanical skiving, score lines or the like.
The invention is based in part on the discovery that by imparting an appropriate longitudinal peel strength to a PTFE sheath, the sheath can be readily split as desired without the need for any type of mechanical skiving along the sheath length. Preferred peel strengths to provide such longitudinal splitting are disclosed below.
An appropriate peel strength is suitably imparted to a sheath by a controlled curing process, sometimes referred to herein as xe2x80x9cprecision sinteringxe2x80x9d. Thus, temperature and cure times are selected to provide the appropriate peel strength. Optimal temperature and cure conditions will vary among specific cure systems. That is, cure conditions may vary with the type of heat source (e.g. radiant or convective heating), residence or exposure times of the PTFE sheath material to the heat source(s), size (e.g. French) of the sheath material being cured, and the like. See the examples which follow for exemplary suitable cure conditions for the described systems. Suitable cure conditions for any particular heating system and sheath material also can be readily determined empirically, i.e. a sheath material can be exposed to alternative cure conditions until conditions are identified that provide a desired peel strength. In other words, cure conditions can be applied, and the peel strength of the cured strength measured to determine if those conditions did in fact provide a targeted peel strength value. If the peel strength is not appropriate, the cure conditions are simply varied until a desired peel strength is provided.
Sheaths of the invention are useful for medical device applications, particularly for use in inserting an ancilliary medical device, e.g., a catheter, guide wire and the like, into a patient.
PTFE sheaths of the invention suitably may be of single layer or multiple layer constructions.
Preferred multi-layer devices afford significant advantages over the devices of the prior art. In one preferred multi-layer sheath of the invention, the outer layer comprises a thermally stable, colored pigment while at least one of the inner layers of the sheath comprises a detectable component, e.g. a radiopaque material for external visualization by X-ray or fluoroscopic procedures.
Using such a multi-layer configuration, no discoloration of the sheath is observed following conventional thermal tipping processes. Thus, devices of the present invention may be produced in a variety of colors, e.g., white, blue or any other thermally stable color, without sacrificing the radiopaque feature of the device.
The present invention also provides methods for manufacturing single or multi-layer peelable sheaths for use as cannulas and other medical introducer devices. Methods of the present invention incorporate extrusion followed by a precision sintering process as generally discussed above in order to achieve optimally cured tubing for use as a peelable sheath. Thus, there is no need to mechanically skive the wall of the tubing to present a weakened, predetermined break line.
Preferred methods for single layer sheath manufacture include: providing a preform PTFE material; extruding the PTFE material into tubing using conventional extrusion procedures; drying the tubing; and imparting a desired peel strength to the sheath that enables facile longitudinal splitting of the sheath without any type of mechanical skiving of the sheath. Precision sintering cure conditions are suitably employed to impart a desired peel strength. A detectable material may be added to the preform PTFE material in an amount sufficient to facilitate external visualization. Preferably, the detectable material comprises a radiopaque material for visualization by X-ray or fluoroscopic procedures.
Preferred methods for multiple layer sheath manufacture include the following: providing a first PTFE material blend for forming the inner layer of the sheath; preparing a second PTFE material for forming the outer layer of the sheath; combining the first and second PTFE materials blends into a two layer preform; extruding the two layer preform into tubing using conventional extrusion procedures; drying the tubing; and imparting a desired peel strength to the sheath that enables facile longitudinal splitting of the sheath without any type of mechanical skiving of the sheath. Precision sintering cure conditions are suitably employed to impart a desired peel strength.
A number of inner layer preform materials may be provided depending upon the number of inner layers desired, i.e. the multiple layer sheath may have 2 or more layers, typically 2, 3, 4 or 5 total layers. Again, a detectable material may be added to one of the preform materials in an amount sufficient to facilitate external visualization. Preferably, the detectable material comprises a radiopaque material for visualization by X-ray or fluoroscopic procedures.
Additionally, different colored pigments may be added to each of the outer and inner layer preform blends. In that way, though inseparable, the layers may be visibly distinguished.
A hub unit is preferably attached to either the single layer or multiple layer sheath on the sheath proximal end to facilitates splitting of the sheath upon application of an effective shearing force thereon. For example, preferred hub may have opposed outwardly extending xe2x80x9cwingxe2x80x9d portions that can be manipulated (e.g. downward or inward pressure) to facilitate longitudinal splitting of the sheath.
The sheath is also preferably tipped at the distal end thereof, e.g., using conventional thermal tipping processes.
Methods of introducing an ancilliary medical device, e.g., catheter or guidewire, using a device of the present invention generally include: inserting a needle or dilator assembly into the bore of a peelable sheath constructed in accordance with the present invention; piercing and dilating the vasculature of the patient using such an assembly; withdrawing the needle or dilator assembly from the sheath component of the device; inserting the catheter or guide wire through the bore of the sheath to the desired target location; applying outwardly cooperating forces to the hub unit, e.g., via attached wing portions, to axially shear the sheath; and removing the sheath from the vasculature of the patient.
Using methods of the present invention, single or multi-layer peelable sheaths are provided that facilitate easy, non-traumatic removal of the sheath following insertion of the ancilliary medical device.
Other aspects of the invention are discussed infra.